Rain Water Collection

water supply Nov 10, 2020

Being in control of your water supply is imperative. There are multiple ways that this can be accomplished. For some great examples, read some of my other posts.  In addition,  rain water collection is a fantastic way to accomplish this even if you live in the the city.  As you will learn from the information below, there is a lot more to this than simply putting out a rain barrel, that is if you are serious about collecting water.  There is a lot of information here to digest.  Enjoy!

Table of Contents


A Short History of Rain Water Collection 

Rain water collection is a concept that has been around for thousands of years. In fact during the time of the Roman Empire, rain water collection was something of an art.  One of the most impressive rain water catchments can be found in the Sunken Palace in Istanbul.  If you want to read a short post about this famous cistern, read this article about the  sunken palace of Istanbul. 

In more modern times as communities, towns, and cites started to grow, new methods of water deliver were needed.  Consequently, the collection of rain water became much less popular with increased urbanization and due to the development of reservoirs and water pipes. Furthermore, with the prospect of spreading disease, many communities ceased the practice altogether.  Eventually the need for organized rain water collection just did not exist except in countries where the climate dictated it due to limited water supply. 

Now in more modern times, for various reasons the concept of rain water collection is being revisited.  With climate change more people are becoming aware that rain water is a vast untapped resource that is essentially going to waste.  

Smaller rain water collection systems are as simple as collecting water into a few barrels. However,  it can also be an extensive system designed to collect enough water sufficient to supply an entire household.

The simple fact is that rain water collection is a viable alternative for supplying water. The technology and resources are available to set up a system capable of supplying a household or a business with a sustainable source of clean water. Consequently, you can easily take control of your own water supply even in an urban setting.    

What is rainwater collection?

In ancient times rain water collection was a vast network of stone gutters, aqua ducts, and rock catchment basins. Today, rain water collection typically refers to collecting run off from the roof of a structure. Water runs into the roof gutters, through the down spout and then into a collection container where it is stored and used at a later time. Even though the traditional means of collecting rain water is from a roof, any sort of impervious surface can be used. Although farms in drier climates have much more extensive collection systems the basic concept still remains the same

Benefits of rain water collection

  1. Reduces your water bills:

Water from roof run off that is collected and stored in large cisterns without any special treatment is used for various non-drinking purposes.  For example, washing cars, washing dishes, watering the garden, flushing toilets, and washing clothes.  Water used for these purposes does not need to be purified.  Flushing the toilet alone accounts for up to 35% of household water usage. Depending on your usage habits, using rain water from a reserve tank can reduce your water bill by as much as 40% to 50%.

  1. Low Maintenance:  

Rain water collection systems are based on simple technology.  Installation, operation, and maintenance are inexpensive. For the sake of comparison, the overall cost of installation and maintenance of water purifying and pumping systems (aka city water) is very high. 

  1. Reduces run off and erosion: 

Run off water occurs when the rate of precipitation exceeds the ability of the soil to soak up that water. Impervious surfaces such as driveways, sidewalks, and streets prevents rainwater from naturally infiltrating the soil. This leads to even more run off.  Excess run off promotes erosion. Harvesting and storing rainwater can, at least in a small way, prevent excess run off and the resulting erosion.  By storing the excess water and using it a little at a time, it is then slowly released back into the environment.  

  1. Reduces demand on ground water:  

As the population grows and urbanization increases, so does the demand on ground water.  In many cases, water is actually pumped out of enormous, natural cisterns and diverted to natural drainage systems and into the city water supply.  The end result is that two different ecosystems are effected.  Albeit in a small way, the collection and usage of rain water reduces the demand on ground water. 

  1. Suitable for irrigation and landscaping:  

Rain water is free of the many contaminates, salts, and minerals that are potentially found in ground water.  Consequently, it is much more suitable for irrigation.  Additionally, since most rooftops make a suitable catchment system, little infrastructure is needed to collect and distribute rainwater.  This in turn reduces the need for fuel based machinery for water distribution.

  1. Reduces groundwater contamination: 

Rivers, lakes, and ponds are dependent on the surrounding watershed for a consistent supply of clean water.  In urban areas storm water is unable to soak into the ground and runs over pavement and concrete. Consequently, the subsequent contamination ends up in the local water supply. Rain water collection will help to reduce this problem.

  1. A natural source of drinking water:  

Rain water is free of the many contaminates that can potentially be found in ground water. Although it can be used as drinking water, it must be filtered and purified. On the other hand, rain water may not contain many trace elements that are actually healthy.  That said, this problem is easily resolved by adding these elements to the water. 

  1. Promotes self sufficiency: 

In my mind, everything you can do to make you less dependent on the local infrastructure is one more step toward personal independence. Collecting and using rain water is another way to manage your own resources. By doing so, you are much more aware of your daily water usage. Consequently, you will tend to focus on the conservation of those resources. 

  1. Collection systems are flexible: 

Rain water collection systems are easily retrofitted to fit any existing structure or incorporated into a new building.  Systems are often designed to be modular, which allows for expansion, reconfiguration, or relocation if necessary.  

  1. Back up water source: 

Whether you are connected to city water or using a well, rain water collection serves as a back up source in the event of an emergency and local water becomes contaminated.

  1. Environmentally responsible:  

When you consider population growth and water shortages, the thought of using tap water to flush toilets and water the lawn is simply irresponsible.  Rain water makes a good alternative. 

  1. Can be used for rain gardens: 

A rain garden is also called a storm water garden. It is another approach to rain water harvesting. Storm water is simply collected to help prevent flooding and erosion.  It is important to differentiate this from other types of gardens. It is not a water garden, a pond, a wetland, or a vegetable garden. It is actually dry most of the time. A rain garden typically holds water for a short period of time after each rain event. 

A rain garden is usually constructed on a downslope. Six to twelve inches of soil is removed and replaced with tillage, sand, or compost to increase the water infiltration. Native scrubs, perennials, and flowers are then planted in the small depression.  It is designed to temporarily hold rain water run off from patios, sidewalks, driveways, etc.  Rain gardens will drain in 12 to 48 hours which prevents the breeding of mosquitoes. 

Disadvantages of Rain Water Collection

  1. Initial cost of set up:

Depending on the size of the system and the technology used, set up cost can be from $200 to $2000. What makes the difference in cost is whether or not portions of the system are underground, such as the storage tanks. As a general rule, the set up cost for most residential applications is low. Once you are past the initial investment, which can be recovered over a number of years, the water is essentially free. 

  1. Unpredictable rainfall: 

Of course the amount of rainfall is difficult to predict. Consequently, if you are in an area where rainfall is generally limited, you should not depend on this resource as your sole source of water. 

  1. Regular maintenance: 

Rainwater collection systems that are unattended become contaminated with debris, mosquitoes, other types of insects, reptiles, and algae.  Although maintenance is not difficult, nor is it expensive, the system must be maintained and cleaned regularly.

  1. Storage limits: 

Most residential systems are going to have a limit to the amount of water that can be stored. Consequently, during periods of heavy rainfall, a lot of water can still go to waste.

  1. Not all roofing material is suitable for rainwater collection:  

Certain types of roofing material will seep chemicals and debris into the rain water.  For example, an asphalt roof commonly sheds particles into the run-off water. Wood shingles are treated with chemicals for preservation and will seep those chemicals into the water.

How to Calculate Your Rain Water Collection

It is a simple process to calculate the total amount of rain water collected by using the following formula: 

1.0 inch of rainfall over 1 square foot = .623 gallons of water


1.0 inch of rainfall over a 1000 square foot roof = 623 gallons of water

The Basic Concept

  • Measure the square footage of the roof being used to collect water. 
  • Find the annual average precipitation for your area. For the United States, go here. 
  • Annual precipitation in inches x square footage of roof = yearly total collection of water in gallons. 
  • For any given rainfall event, use this easy formula: 

Amount of water   =  catchment area     x     rainfall         x         0.623

     collected                           square                        depth                  conversion 

     (gallons)                              feet                          (inches)                  factor

Legalities of Rain Water Collection

As is usually the case, there are laws regulating everything we do.  

In the end, you have to make your own decision regarding what you do and how you do it.  That includes harvesting rain water.  However, it is best to be educated on the local laws.  Each state is different.  Some states prohibit rain water collection altogether.  However, the good news is that many of these states are beginning to relax their regulations.  

That said, I strongly advise you to educate yourself on local regulations.  The National Conference of State Legislation has a nice summary on the laws in each state.  

Methods of Rain Water Collection

There are numerous articles on the internet discussing all the different methods of rain water collection. For example, “27 different ways to collect rainwater”. While these articles do make for interesting reading, the basics of rainwater collection remain the same.  That is the beauty of it. The set up and technology is simple. The only thing that differs is the scale of the system, what you are attempting to accomplish, and the conservation effectiveness of each system. This of course makes a huge difference in the equipment and technology that is needed. But the best part is that rain water systems can be scaled according to your budget.    

Another simple but important consideration is where you purchase materials. Using “rain barrels” has become much more socially acceptable. Consequently, you can purchase what I call “boutique barrels” from your local home improvement store or garden supply outlet and pay a considerable amount of money for them.  Or you can accomplish the same thing by purchasing 55 gallon food grade plastic drums off of eBay or Craigslist for dirt cheap. Additionally,  large food grade caged containers, called IBC tote tanks, hold several hundred gallons. I purchased two 275 gallon food grade containers for $125 each including delivery.

General tips for setting up a rain water collection system:

  • The easiest drainage surface to use is a roof.  Most people collect water from the roof of their house. But, the roof of a shed, garage, or some other structure also works.  
  • Make sure the roof structure is clean.  Metal roofs are best.  Shingled roofs tend to shed small particles of roofing material. This is not a problem if you are not going to drink the water. 
  • Keep the gutters and down spout as clean as possible.
  • Place a fine screen over the entry point of the water collection container. This will filter out larger debris and keep the water cleaner. 
  • Place a spigot or other valved device at the bottom edge of the collection container so that water can be drained.
  • Elevating the collection container makes it easier to drain the water into a smaller container.
  • Make sure your collection container is placed in a semi-permanent location so that it does not have to be moved.  Keep in mind that a 55 gallon drum of water is going to weigh about 460 lbs. 
  • If you are going to drink the water, the type of roof you have makes a difference. Avoid shingles, wooden shakes, or metal flashing that may contain lead. A metal roof is best. Additionally, the collection container needs to be food grade. Anything else will leach chemicals into the water.  Do not be tempted to use an inexpensive 55 gallon trash can. 

Components of a Rain Water Collection System

The basic components of a collection system are the same.  The only difference is the scale of the system.  The components are as follows: 

  • Catchment (drainage) surface
  • Delivery system (to the storage container)
  • Storage 
  • Treatment
  • Distribution equipment

Keep in mind that these systems can be as simple or as complex as you want to make it depending on what you are trying to accomplish.  

1) Catchment or drainage surface

The typical drainage surface is the roof of some existing structure. Taking advantage of an existing roof simply keeps the cost of infrastructure at a minimum. However, any impervious surface will work. 

If you are using a roof for a catchment area, there are three things to consider: materials, slope, and size.

  • Materials

Each type of roofing material has obvious advantages and disadvantages when it comes to rain water collection.  If you are starting from scratch, a metal roof is the best material to use if you collecting drinking water. That said, all roofing materials are going to produce some type of contamination. No material is perfect. Furthermore, weather conditions constantly cause deterioration of any roofing material. That deterioration  can promote contamination. The table below lists some of the more common types of roofing material and the potential contamination.  

General summary of common contaminants in rain water by type of roofing material. 


Type of roofing material Common contaminants Recommended usage
Galvanized metal roofing Copper, lead, high levels of Zinc  
Sheet roofing (PVC)   Non-Potable use only


clay, ceramic, cement, fiberglass

Copper, lead, zinc Non-Potable use only


asphalt, composits, three tab asphalt)

May contain low levels of asbestos if manufactured before 1980 Non-Potable use only


cedar shakes/wood

Support mold, algae, insects, may be treated with fire retardant or other chemicals Irrigation only
Plywood covered with roofing paper and tar Copper, Lead, Zinc  


Perhaps the most definitive study on this subject was conducted by the Texas Water Development Board. They published an extensive document which is available to the public. Download their  PDF here.  

Besides the roofing material itself, the second greatest source of contaminants to rain water is what lands on the roof. The combination of wind, animals, traffic, debris from plant life, as well as many other human activities results in a large amount of dirt and debris ending up on your roof. 

Conclusion on Contaminants 

Rain water collected from any roof is always going to contain a certain amount of contaminants, including various fecal coliforms. You may as well accept that up front.  Unless you happen to live in an area that historically has not had any modern agriculture, manufacturing, transportation, mining, or industrial activity within 25 miles you are going to have to accept the fact that the water will be contaminated. If you plan on using the water for drinking purposes, then filter and treat it appropriately. 

CAUTION: A combined study conducted by the Cockerel School of Engineering and the Texas Water Development Board looked at the range of possible pollutants from each roof type.  This study noted that rain water collected from roof tops has a high concentration of dissolved organic carbon (DOC). This substance in-and-of-itself is harmless.  However, when combined with chlorine, which is commonly used to disinfect drinking water, DOC can combine with chlorine to form potentially hazardous carcinogenic (cancer causing) compounds.

If you want to read the post on this, visit the Earth Times and read their article on roofing for rain. 

  • Slope of the catchment area

The steeper the slope, the faster the water will run off.  This means that every time it rains, the faster flow of water will help to clean the roof surface of contaminants. Flatter roofs have much more of a tendency to retain debris even after a good hard rain.  

  • Size (footprint) of the catchment area

The size of the roof (catchment area) determines how much water you can harvest during each rain event. If the building being used has no overhang to the roof, then simply measure the square footage of the exterior. This will give you a good approximation of the square footage of the roof. If there is an overhang, you will need to include that as well.   It should be noted that the shape of the roof makes little difference in the “foot print” of the roof structure.  Consequently, if the roof on the structure in question is an odd shape and has multiple angles, this is going to make little difference in the water harvested.

2) Delivery system

The water delivery systems is also referred to as the conveyance system.

This simply refers to the gutters, pipes, and downspouts that carries the water from the surface of the roof to the storage container. The design of this portion of the system needs to account for proper sizing, installation, and aesthetics.

  • Sizing

Sizing of a rainwater collection system will drastically affect the cost. A small increase in the size of components, such as plumbing,  will substantially influence  the total cost of the system.  

Gutters: As a general rule, gutters should be at least 5 inches wide. Plan for a 100 year rain event. Coastal areas are generally going to have more intense rain events that inland areas. 

Downspouts: For every 100 square feet of roof area, plan on one square inch of downspout. For example, a 2 inch by 4 inch downspout (8 square inches) will accommodate run off from an 800 square foot roof. A 3 inch by 4 inch (12 square inches) will accommodate run off from a 1200 square foot roof. This same rule can be applied to circular piping such as PVC. 

  • Installation

Proper installation is important for things to function correctly and safely. Gutters need to be sloped 1/16 inch per foot to provide adequate drainage. Gutter hangers need to be placed every three feet or every foot in areas of heavy snow.  Components should be painted to prevent degradation from UV exposure.  

  • Aesthetics

This is truly a matter of personal choice. Most gutters can easily be matched to the color of the structure.  PVC piping can simply be painted.   

3) Storage

There are several important considerations when it comes to a storage container for rain water. It is important to read through all of this material prior to making a decision on the type of tank and how it is installed.  Consider the following: 

  • Safety considerations
  • Tank material
  • Color
  • Costs
  • Connections (inlet, outlet, other openings)
  • Connecting multiple tanks
  • Site planning
  • Safety Considerations

Make certain that the tank is safely installed. You may need to seek advice from the Occupational Safety and Health Administration (OSHA) regarding installation. 

Unintentional access by anyone must be prevented.  If the tank or cistern is above ground it either needs to be tall enough to prevent access or the lid must be locked.  

Good water quality must be maintained.  This means the tank must be colored appropriately to prevent light penetration.  Sunlight promotes the growth of algae. All openings must be screened to prevent entrance by animals and insects. 


  • Tank Material

There are numerous materials available for water storage. Cost is widely variable and each material has its own pros and cons.  

Plastic tanks are the most common application for a residential rain water system. They are light weight, affordable, and come in many sizes, shapes, and colors. 

Fiber glass tanks are very versatile. These tanks are rigid and fairly lightweight. Installation can be above or below ground. 

Concrete tanks are also very versatile. They are very heavy but very strong. Installation can be either above or below ground.  Due to the weight, concrete tanks are either poured at the site or prefabricated and assembled at the site. One advantage to concrete is that it raises the pH of the rainwater and neutralizes the natural acidity.  

Formed metal tanks are typically prefabricated and shipped as a whole unit. Consequently, they are more expensive.  They are either sealed on the inside or lined with a water proof material.  

Corrugated steel tanks are easily available and affordable. They come in a large range of sizes and are typically assembled on site. Once assembled they are lined with a vinyl material which makes them waterproof.  

  • Color

The main purpose of tank color is to protect water quality.  Clear or translucent tanks allow for the penetration of sunlight, which promotes the growth of algae. Tank color also affects water temperature.  Lighter colored tanks reflect sun light and thus reduces the temperature of the water. Tank color also affects aesthetics, which may only be a concern in public areas.  

  • Costs

The cost of a tank is going to vary greatly depending on the size, material, shipping and assembly.  Some of this was discussed in the materials section above. Size your system appropriately and do your homework before spending any money.  

  • Connections and openings (inlets, outlets, and other openings)

Every rain water storage tank should be equipped with an inlet, outlet, overflow, vent, and an inspection or service port.  

The inlet is where the water enters the tank from the delivery system.  This needs to be equipped with a calming inlet, which controls the inflow of water. Additionally, it helps to introduce oxygen and prevent swirling, which in turn prevents the disturbance of the fine sediment at the bottom of the tank.  

The outlet is where water leaves the storage tank for end use. This is mostly commonly placed at the bottom of the tank to take advantage of gravity flow.  The outlet is generally placed at least four inches from the bottom to prevent draining any sediment.  Another option is to use a floating tank pickup. This device drains water from the top four inches of the tank. 

Regardless of the size of your system, there must be an overflow to divert excess water during heavy rain.  The overflow is placed slightly below the inlet. Additionally, a vent is necessary to prevent a vacuum from forming inside the tank. Keep in mind that vents and overflows must be screened to prevent insects and small animals from entering the tank.  

Lastly, the inspection port should be at the top of the tank. The inlet at the top of the tank can also double as the inspection port.  This should be large enough to allow someone to enter the tank for inspection, cleaning, or any other maintenance. 

  • Connecting multiple tanks

There are two common ways to do this. The first way is to connect the tanks at the top. The overflow from one tank diverts water to the inlet for the next tank in line.  The second way is to connect the tanks at the bottom.  This means that each tank is filled to the same level.  If this type of system is used, there must be an isolation valve for each tank.  This prevents the entire system from draining in the event that one tank develops a leak.  

  • Site planning

Proper planning of the installation is imperative. This is because once a storage container is in place it may be all but impossible to move it or make substantial changes to the system. Some important considerations for installing the storage system as as follows: 

  • Before installing one tank, allow additional space for other tanks in the event you need to expand. 
  • Place the tank on a solid surface that will not settle.  Water is heavy. One hundreds gallons weighs slightly less than 900 pounds. Keep that in mind and make certain to place the tank on a solid surface. 
  • Minimize the distance between the downspout and the tank.
  • Place the tank as close to the end use area as possible (gardens, plants, livestock water containers)
  • Elevate an above ground tank and take advantage of gravity for water flow.   
  • Below ground tanks are more expensive for several reasons.  They are more difficult to install, maintain, and remove if needed.  They are also more difficult to inspect and clean.  One advantage to an underground tank is that the water stays at a near constant temperature.  
  • Above ground tanks are a lot less expensive.  However, they are more subject to adverse weather conditions (freezing) and deterioration due to exposure to sunlight. They can also take up a lot of space. 

4) Treatment of Rain Water

Rain water is generally considered to be clean simply because of the natural way it is formed. However, rain water is a relatively strong solvent due to it’s pH, generally around 5.5, which is acidic. Once rain water comes in contact with your roof, it becomes contaminated with chemical, metal, and microbial components. But, the type of contamination does to some degree depend on your geographical location. Because it is nearly impossible to prevent some sort of contamination when collecting rain water, you have to plan for this and treat the water accordingly.

Treatment prior to storage

Debris is going to collect on a roof surface between rain events.  The first portion of the rain to come off the roof is essentially flushing the roof surface.  Consequently, that first portion of drainage is going to contain most of the accumulated debris. This necessitates filtering the rain water prior to entering the storage container. This can be accomplished in several different ways: 

  • First flush diverter: This device initially diverts water away from the storage container and catches all of the debris. The general recommendation is about 2 gallons of diversion for every 100 square foot of roof surface.  
  • Gutter screens: These screens prevent the debris from even entering the system. They should be cleaned after each rain to prevent clogging.  
  • Downspout screen: These screens remove large debris that flows down from the gutters.
  • Inlet/inspection port screen. This is a basket type screen that fits into the inlet. It should be cleaned after each rain. 

Treatment after storage  

How the rain water is treated after it is stored depends on the intended use.  Using rain water for potable purposes requires a different level of treatment versus using the same water for gardens, household plants or irrigation. Best practice is to plan for a multi-stage treatment process.  This usually involves filtration followed by disinfection. 

  • Filtration

Similar material was discussed in the chapter on How to Maintain a Safe Water Supply.   If you remember, water filters are designed to filter out microscopic components such as bacteria, protozoa, viruses and fine sediment. Microscopic pathogens vary in size so it it important to choose an appropriate filter based on the intended use. 

Filter size is usually discussed in terms of microns (one millionth of a meter). So, a 4 micron filter will remove particles that are 4 microns or larger.  Review the section on filter sizing in the chapter on How to Maintain a Safe Water Supply. 

  • Disinfection

The main purpose of disinfection is to neutralize or kill microscopic organisms that cause illness.  Not all filters are capable of removing small organisms such as bacteria, protozoa, and viruses. Even if your filter is capable of this function, disinfection provides an additional safety margin. 

Chlorination is a widely accepted form of disinfection. Chlorine comes in several forms so be sure to use something that is recommended for potable water. The additional advantage of chlorine is that is also provides residual disinfection of water delivery components such as plumbing. 

Ultraviolet light (UV) is also a widely used form of disinfection. When organisms are exposed to UV, they are inactivated and become incapable of reproducing or causing disease.  Scientific evidence has shown that UV light is effective against a significant variety of bacteria, protozoa, and viruses. This includes the organism responsible to typhoid, polio, cholera, and hepatitis. UV is also effective against Giardia and Cryptosporidium.  

One distinct disadvantage to UV disinfection is that the effectiveness is diminished if the water if turbid, cloudy, and contains significant sediment.  Therefore, filtering the water prior to UV exposure is best practice.  

For more information, read this PDF  on UV disinfection. 

Ozone gas is another possible means of disinfection. Ozone gas, similar to chlorine, is a strong oxidizing agent. It is a colorless gas that disinfects, deodorizes, oxidizes, and clears the water.  

There are many advantages and disadvantages to using this method.  However, it must be installed by a licensed professional.  For a great article on the pros and cons of using this method go here. 

Absorption filters, in particular carbon filters, are widely used in homes because of their ability to remove disagreeable tastes, odors, and even chlorine.  Activated carbon also removes many chemicals.  However, it will not remove heavy metals nor will it alter the hardness of the water. The big advantage of carbon filters is their high capacity, which means they last a long time. 

Best Practice

The bottom line is that the best way to produce safe water is to filter the water first then follow that with disinfection. It is typically a two stage process. For rain water in particular, gross filtration occurs with the removal of large debris prior to entry into the storage container. That is followed by fine filtration of microscopic contents, which removes microbiological elements and fine sediment.  Then disinfection occurs.  The end result is purified, potable water.  

Important note: Water that is processed in this manner, rain water in particular, has a lack of trace elements that are important to good health.  If you are consuming this water on a long-term basis, it is imperative to add trace element supplements to that water.  These can easily be purchased online. 

5) Distribution Equipment

Distribution equipment includes plumbing, drip systems, pumps, pressure tanks, and back flow devices. 

Important note: As you will see, it is imperative to complete the design of your distribution system prior to starting the installation.  System requirements will vary greatly depending on the intended use. Forethought and planning will save you a considerable amount of money. 

If you are only using gravity flow, then the distribution system is very simple. All that is needed is the proper plumbing and drip system needed to produce limited water flow to the point of use (watering plants, etc.) However, if you plan to bring water into your home or cabin, this will require the services of a licensed plumber.  Since this will be water delivered under pressure, the key components are as follows: 

  • plumbing
  • water pump
  • pressure tank
  • Back flow devices

The plumbing needed will depend on the pressure that is required to delivery the water and the intended use.  Things such as shower heads often required only 30 psi (pounds per square inch) of pressure and 2.5 gallons per minute (volume). It is also necessary to account for the total pressure and volume for all of the intended uses, such as the shower head, toilet, kitchen sink, clothes washer, etc.  The plumbing must be able to withstand the required pressures without rupturing or leaking.  

When selecting a water pump there are several parameters to consider:

  • Type of water to be pumped. Some pumps are designed to push dirty water that contains a lot of debris. Others are designed to pump only clean water.  If you are transporting potable water for in-home use, then you need a pump designed to delivery clean water, NOT a sewage pump. 
  • Volume to be delivered. Pumps are rated for a maximum volume of gallons/minutes or gallons/hour that can be delivered.  The amount of water to be delivered will vary according to the requirements of the system you design. 
  • Pressure. Each pump has a maximum PSI (in line pressure) that can be produced.  For example, if you need 30 psi for a shower head, then you need a pump that will produce at least that much in-line pressure (actual pressure inside the plumbing) 
  • Intended operating time. Water pumps are typically rated for continuous or intermittent use.  For example, a pump that circulates water in a swimming pool is being used continuously. A pump in a recreational vehicle that delivers water to a shower or sink is used intermittently. A pump designed for household use will be used intermittently. 
  • Self priming or not.  Pumps drive water by means of an impeller. An impeller is essentially an internal paddle, water wheel, turbine, that turns rapidly and produces forward water flow. Some pumps have to be primed before use, meaning you have to add water to the impeller housing through a port before starting the pump. Others are self priming. This means the impeller housing can be run dry for a period of time and will produce enough suction to bring water into the housing.  If water is fed to the pump via gravity, then the impeller housing will likely always be wet and the pump does not have to be self priming.  If you are pumping water vertically out of a tank, then the impeller housing will be dry. This situation requires a self priming pump. Another practical option when pumping water out of a tank is to use a submersible pump.  
  • Voltage requirements. Water pump voltage needs to match the voltage of your electrical system.  If you are on the grid, then it must match your household voltage.  If you are off the grid, then it needs to match the voltage of your solar electric system. Depending on your solar design, your system voltage can be 12 volt, 24 volt, or 48 volt. So, shop for a pump according to your system design. 

The next system component to consider is a pressure tank. It is not necessary to use a pressure tank but the clear advantage is that it will reduce the wear and tear on the water pump. For example, most households are going to have intermittent demands for water throughout the day. This occurs as you run water into the sink for dishes, take a shower, or flush the toilet. Consequently, the pump must turn on and off throughout the day, which produces a higher demand on the pump and results in more wear and tear on the equipment. With a pressure tank, a given amount of water is stored under pressure.  As the water is used the pressure in the tank drops. The pump turns on as needed to refill the tank. Consequently, the life of the water pump is greatly extended.  

Lastly, if you are going to pump rain water into existing plumbing that is connected to a municipal water supply, you may be required to install back flow devices. Thisprevents rain water from back flowing into municipal water causing potential contamination.  These devices are generally regulated by local laws and ordinances.  

Final Words on Rain Water Collection 

This is a lot of information to consider, probably more than you thought. Right about now you are likely feeling overwhelmed. Just keep in mind that the design of a rain water collection system can be as simple or complicated as you want it to be. Design and install something that is suitable for your lifestyle, something that you will be happy with, as well as something that is within your budget. 

Additional Posts of Interest

How to Choose the Best Water Filter

How to Maintain a Safe Water Supply

Go off grid and live well, 


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